getVal

Get the value of a "double" maintained by this xholon instance.
If a class that implements this interface does not maintain such a value, it should return 0.0
This method can be used in place of getVal_double()

setAttributeVal

Set the value of an attribute, given it's name.
The default implementation of this should handle any variable with the name "val".
Concrete subclasses may handle any other variables, which would be required if using JavaMicro reflection.